Preparation of cyclic hydrocarbons



Oct. 30, 1945. A. l.. FOSTER 2,387,989

PREPARATION OF CYCLIG HYDROGARBONS Oct. 30, 1945.

A. L. FOSTER PREPARATION OF CYCLIC HYDROCARBONS Filed June 12, 1942 2 Sheets-Sheet 2 YPatented Oct. 30, 1945 PREPARATION F CYCLIC HY DROCARBONS Arch L. Foster, Bartlesville; Okla., assigner to Phillips Petroleum Company, a corporation o! Application June l2, 1942, Serial No. 446.752

3 Claims.

This invention pertains generally to the changing of molecular structure of hydrocarbons to produce materials more suitable and eiilcient for commercial and industrial purposes. It relates more specically to the cyclization, including aromatzation, of light petroleum and natural gas hydrocarbons to obtain hydrocarbons oi different boiling ranges and higher anti-knock rating for use in, for example, improved aviation and motor fuels.

It has long been known in the art that diierences in molecular structure of fue] hydrocarbons affect remarkably the performance oi the hydrocarbons in internal-combustion engines. The rate and nature ot combustion of a hydrocarbon `of any given molecular weight or carbon-hydrogen composition varies with the structure or molecular coniiguration of that hydrocarbon. In general, the more complex the molecule, the higher the resistance to detonation when the material is burned under the conditions oi elevated temperature and pressure as exist in the cylinder of the internal-combustion engine during the compression and combustion parts of the cycle. The lowest degree of resistance to detonation under these conditions is possessed by straightchain aliphatic hydrocarbons, such asl for example, normal heptane, having the carbon atoms connected in a straight chain or line, C-C-C- C-C-C-C, in which no tertiary carbon atom is present, that is, no carbon atom is directly connected to more than two other carbon atoms. If this normal paramn is changed so that one or more carbon atoms are present as side chains, that is, where one or more carbon atoms are tertiary-connected to three other carbon atomsthe resistance to detonation is increased by this change in conguration. As more and more side chains are formed at the expense of the main parailin chain, the higher becomes the resistance to detonation, that is, the higher the anti-knock quality of the hydrocarbon. To illustrate; normal hexane, C-C-C-G-C-(J, has a very low anti-knock rating or octane number on the at present standard A. S. T. M, octane scale as is l employed internationally for evaluating relative degrees of tendency to knock under engine operating conditions. The isomeric hexanes, of which there are tive, exhibit progressively greater resistance to detonation as the molecule of six carbon atoms becomes more complex, until the isomer neohexane,

chgo o rates approximately 95 on the current standard A. S. T. M. scale. Cyclohexane, in which the six carbon atoms are conjoined in a closed ring and which two hydrogen atoms less than the Cil (Cl. 2ML-673.5)

corresponding acyclic or non-cyclic paraillns, is rated at about to 80 on this same scale, making the cycloparainn a greatly improved ingredient of motor and aviation fuels as compared tok the normal, straight-chain hexane structure.

Aromatic hydrocarbons. containing a given number of carbon atoms in a specic and peculiar ring structure, but possessing a smaller number of hydrogen atoms than are found in either the cycloparaiiins or the straight-chain or isomeric parailns. also possess to a remarkable degree the property of resisting detonation in the automotive engine. The typical structure o! the aromatic hydrocarbon is that of benzene in which six carbon atoms are arranged in a ring structure, but which contains only six hydrogen atoms, or six less than does cyclohexane withthe same number of carbon atoms. This peculiar condition of unsaturation without the existence of olenic bondsaccording to the best accepted theories-imparts to aromatics peculiar properties, especially those of resistance to detonation as a motor fuel, and high reactivity of the hydrogen atoms present in the aromatic nucleus.

Aromatic hydrocarbons are important raw materials i'or the synthesis of a host of important chemical products, and their preparation from petroleum hydrocarbons is increasing rapidly in importance. An increasingly large proportion of the total aromatic hydrocarbon production is derived from petroleum sources, by synthetic methods. Cycloparaflins, also, are becoming more and more important as starting materials for chemical synthesis and therefore methods for their production or synthesis are increasingly important.

In carbon-hydrogen composition, the cycloparafiin is analogous to the olen, each posssing two hydrogen atoms less than the corresponding parailin, which has the generic formula Cul-Inu. in which n is the number of carbon atoms per molecule. The monooleiin and the cycloparaiiln have the formula CH.. 'I'he cycloparaflln, however, does not possess the double bond between adjacent carbon atoms which characterizes the olefin and does not show the same properties traceable to this state of unsaturation. The cycloparailins may be said to possess properties intermediate between oleiins and saturated parafnns with some of the advantages o! both and less oi the disadvantages of each. especially from the viewpoint of motor and aviation-fuel properties.

The cycloparailin may be prepared from parains or from olens, either by direct dehydrosenation of the parailin and conjunction of the hydrogen-vacated bonds to close the ring, or by formation of oleilnic bonds and later by reallocating these bonds to close the carbon ring. If this dehydrogenation is carried further at the same time, aromatica may be formed containing the benzene nucleus or multiples of it, with or without substitution o! nuclear hydrogen by alkyl or other radicals. It is considered that formation of aromatics takes place in a series of steps, in the case of each molecule so formed. An initial step dehydrogenates the straight-chain parailin to give two unsaturated bonds on terminal carbons cr at least on carbons which, with intermediate carbons in the chain between the carbons sustaining the unsaturation by hydrogen removal, form a six-carbon chain; these unsaturated bonds unite to form a cycloparailin ring. Further dehydrogenation then removes, apparently preferentially, one of the two hydrogen atoms on each of the ring carbons, producing the peculiar state oi' unsaturation without olefinic double bonds which characterizes the aromatic molecule.

The preparation of cyclics. i. e., cycloparafiins or aromatics, in accordance with this invention, therefore, is determined not only by the specific conditions and speciiic catalysts employed, but also by the degree and kind of unsaturation produced. It is possible to employ the same catalysts and the same equipment and cycle of operations for the production of cycloparaflins or aromatics, by varying the severity oi' the reaction conditions and the time of exposure o! the charge stock to the conditions. By employing conditions of operation which promote the formation of cycloparaflins, and by stopping the unsaturating reaction when the degree of unsaturation required for forming cyclic parains has been attained, a preponderance o! cycloparafns will be formed at the expense of aromatics formation. In Ipractically any reaction system preparing cycloparai'ns some aromatics are formed as byproduct. These aromatlcs may be isolated from the cycloparatllns and from unreacted charge and puriiled as such, may be recycled to the dehydrogenation zone for reaction with hydrogen therein to form cycloparatiins therefrom, or may be hydrogenated in a separate zone under any desired conditions to cycioparaiiins by the addition of the requisite amount of hydrogen to the aromatic nucleus.

Cyclization of paraiiin hydrocarbons, especially aromatization to form the benzene nucleus and its substituted homologues, can be accomplished by heat and pressure alone, in the absence of catalysts, as a number of commercial processes now in operation attest. However, thermal methods alone are non-speciiic and non-directional and the yield of products other than aromatics and/or cycloparailins may be large. making the cost of the aromatic andi/or cycloparaillnic content excessive. Proper choice of catalysts enables the operator to carry out the process in greater yield, under less severe conditions and with better control over the specic materials produced than can be the case with thermal methods alone.

Analogously, the process may be carried out with one catalyst or a combination of catalysts, one step or two steps. or two catalysts or more may be employed.v If, as theorists believe and as is supported by much research data. cyclization is a combination of dehydrogenation of lparailns followed by ring closure of the resulting olens by juncture of olenic bonds within the individual molecule and consequently is a two-step reaction. it is of advantage to employ two catalysts and two steps or a single catalyst promoting the two reactions under diierent reaction conditions, optimum in each case for the reaction desired in each step. This is done in accordance with my invention.

The principal object of my invention is to provide an improved process for the cyclization of para'lns. Another object is to provide for the carrying out of the cyclization in two separately controlled stages, each of which is controlled to give optimum results in the overall process. Another object is to provide such a process capable of ready application to heavy oils of the general type of cracking stock and involving preliminary catalytic cracking to produce an essentially paraflnic cyclizaton charge. Another object is to provide a process of the foregoing type which utilizes a single catalyst, preferably aluminum chloride or equivalent metal halides, and in a preferred embodiment passes the catalyst countercurrent to the main now and in such manner that the catalyst encounters increasingly severe or stringent reaction conditions of temperature, pressure and contact time. whereby it is active for each successive conversion. Numerous other objects will more fully hereinafter appear.

Fig. 1 of the accompanying drawings is a diagrammatic representation of one arrangement of apparatus for carrying out one embodiment of the present invention.

Fig. 2 is a similar schematic representation of equipment for carrying out the present invention in another embodiment in which a preliminary cracking step is employed and in which a. metal halide, preferably anhydrous aluminum chloride, is used as the catalyst in all zones of the process, being cycled therethrough countercurrently to the iiow o1' hydrocarbons.

In accordance with my invention, in its broadest aspect, the cyclization of Cs or higher parairlns is conducted in two separately controlled catalytic zones. each operated under different and optimum conditions. In the rst zone, which is normally maintained at a higher temperature, the reaction brought about is primarily one of unsaturation or dehydrogenation and conversion to forms which are most readily adapted to ready cyclization to form cycloparaiins and aromatics.

The invention will first be described with reference to the embodiment typled by Fig. l and wherein the dehydrogenation catalyst is different from and used under different conditions from that of Fig. 2.

Among the dehydrogenation catalysts which may be mentioned as emcient in carrying out the preliminary step in my cyclization reaction are the normally solid and liquid salts and oxides of the metallic elements in groups 1V to VI of the periodic table, which are, in ascending order of their comparative activity in dehydrogenation, as follows: Oxides of elements of Group IV-titanium, zirconium, tin and lead, which show the lowest dehydrogenatlon activity in these three groups. Oxides of elements in group V-vanadium, columbium, and tantalum, which in general show higher activity than those of group IV. Oxides of elements of group Vil-chromium, molybdenum, tungsten and uranium, which are the most effective and strongest dehydrogenating catalysts of the three groups. Other metallic oxides show etllciency under suitable conditions but those mentioned serve to illustrate the invention adequately.

In the cyclization-aromatization reaction, increase otcontact time under any given set of conditions increases the likelihood and percentage formation of aromatics at the expense of cycloparafi'lns. Correspondingly. increased temdrocarbon residues.

aaneen peratures increase aromatization. Increase oi pressure with maintenance of lower temperatures and shortening of contact time tend to form cycloparaillns and isomeric parainns at the expense of aromatic formation. In operating this process for the vpreparation of cycloparaiiins and isomers thereof it is desirable to control operating conditions to minimize the excessive dehydrogenation which produces aromatics. Increase in the severity of operating conditions enables the operator at will to increase the aromatica output, giving the invention great iiexibility to meet commercial demands or to produce a desired material from any variation of charge stock which may be available.

As cyclization catalystsanhydrous aluminum halides have shown good eillciency under the proper control of operating conditions. For cost reasons the chloride is generally employed and is preferred in this process, especially in the presence of the aids, diluents and/or promoters as mentioned below. Less desirably, other catalysts may be employed, for example, chlorides of other amphoteric metals, such as ZnClz, FeCla. BeClz. T1014, ZrCl4, SnCh, SbCls, etc. Instead of halides of metals yielding an amphoteric hydroxide, other cyclization catalysts may be used such as zinc oxide, alumina, silica, etc.

Aluminum chloride catalyzes a great variety oi' reactions involving hydrocarbons and its catalytic activity and the products of its catalysis vary widely, depending on the reaction being carried out and the reaction conditions employed. At higher temperatures, of the order of 3'75-4007 C. (about '1D0-750 F.) and above, its action becomes non-specific in regard to products formed, and it eilects essentially a. cracking reaction, decomposing heavier hydrocarbons to form lighter products, along with addition products formed by combination of the chloride molecule with hy- At the lower temperatures, of the order of 95-150 C. f about 20D-300 F.) the temperature depending on the material treated and the pressure employed, parailin hydrocarbons may be dehydrogenated and cyclized with or without rupture of the molecule to form an intermediate oleiin or paraiiln of lower molecular weight. For example, nonane is decomposed at 200-230 F. and low pres'sures to form butane and pentene, which latter cyclizes to form principally cyclopentane. Experiments show that at tem- Peratures within this temperature range, cycloparatfins such as cyclopentane are not reacted on further by aluminum chloride, and therefore cycloparatllns are a desirable end product of the aluminum chloride reaction catalysis in this general temperature range. At still lower temperatures. as from minus 20 to plus 40 C. (minus 4 to plus 104 F.) heavier hydrocarbons are formed from low-molecular-weight olens; thus, naphthenes. poly-naphthenes and alkylsubstituted naphthenes are formed from butenes and homologues, the products boiling mainly from 500 F. upward. Many other examples might be given of the wide variety of products which may be catalyzed by aluminum chloride when temperatures, pressures, contact times, and composition ot charge stocks are controlled satisfactorily, but these specific examples will serve to show the results which may be expected in the process of this invention for the cyclization of paraiilns to cycloparamns and aromatics.

For some reactions so-called nascent AlCls, prepared in situ by introducing into the reaction zone metallic aluminum and anhydrous HCl, ap-

pears to give better results than does the anhydrous salt prepared in the usual commercial manner. This is believed to be due to the effect of the nascent hydrogen liberated during the reaction between the metal and anhydrous acid. Largely the same eil'ect may be obtained by the maintenance of the reaction materials under elevated pressure with molecular hydrogen, or a mixture of light hydrocarbons containing appreciable amounts of molecular hydrogen. The presence of the hydrogen doubtless serves to inhibit polymerization of the olelns intermolecularly, to prevent further dehydrogenation and thus to further intramolecular saturation or cyclization. correspondingly, the presence of appreciable amounts of hydrogen in the reacting materials in the dehydrogenation step aids in controlling the degree of dehydrogenation obtained by approaching more closely, during the reaction period, the equilibrium between olefin and hydrogen content.

I have found that the introduction of an inert gas or vapor as va diluent has a desirable eiect on the reactions, both oi dehydrogenation and of cyclization. Steam, iiue gas or low-molecularweight hydrocarbons, such as methane and ethane, show this eiiect to the desired degree, and may be introduced into the charge stock stream prior to its entry into the reaction chambers, along with the hydrogen. A preferable method is to introduce a light hydrocarbon gas rich in hydrogen into the charge stock before the stock enters the preheater where it is heated to reaction temperature before entering the unsaturator. as will be described in connection with the accompanying drawings. Eiiluent light gases from the i'lnal iractionator, containing light hydrocarbons and the hydrogen released from combination during the dehydrogenation step, may be recycled to the latter step. and the quantity may be augmented by hydrogen and/or hydrocarbons from an outside source, if necessary. More commonly excess gases will be discharged to waste from this line and only that portion required to maintain the required equilibrium in the unsaturator and in tre cyclization chambers to control the degree of reaction occurring therein will be recycled, since a surplus of free hydrogen and of light gases will be built up gradually in the system.

The essential features of the embodiment of Fig. 1 may be summarized as follows. Charge stock containing one or more hydrocarbons containing from 5 to 12 carbon atoms per molecule is introduced, after preheating to a suitable tempcrature, into a catalytic dehydrogenation zone. The temperature maintained in this zone will depend upon a number of factors. Mild dehydrogenating catalysts will require higher temperatures than do more active catalysts. Bauxite or oxides of group IV metals may require temperatures as high as 1200 F., to bring about dehydrogenation to simple monooleilns. Temperatures as low as 500 F. may be used under other circumstances. Temperature, dilution and hydrogen content of the entering charge are so adiusted that conversion is restricted to a maximum degree to monoolefin formation. The determination of that combination of conditions giving op. timum results with aV given stock will be within the skill of workers in the art in the light of the disclosure herein.

More active dehydrogenation catalysts, such as vanadium oxide, chromium oxide, molybdenum oxide and mixtures thereof will require lower temperatures and shorter contact times. The action of a too active catalyst or one which tends to carry dehydrogenation too far or to induce cracking at the higher temperatures or longer contact times, may be alleviated or reduced by the addition of a retarding or less active material such as aluminum oxide, silica, salts, oxides, or hydroxides of alkali or alkaline-earth metals such as potassium, lithium, sodium, rubidium, beryllium, magnesium, calcium, strontium, barium or other basic oxide of elements in groups II and III of the periodic system. Contact time may also be controlled in such manner as to halt the dehydrogenation reaction at the desired point, namely, upon the formation of alpha and beta monoolens to the exclusion of dioleflns, aromatlcs, etc.

'Ihe pressure in the first step may vary widely but will usually be from about 50 to about 1500 pounds per square inch gauge, depending on the temperature maintained, the catalyst, the charge, etc. In some cases. as when using a catalyst consisting of a halide of an amphoteric metal, it may be as low as atmospheric pressure, ranging therefrom up to 100 pounds per square inch gauge since the temperatures are usually more moderate when using such a catalyst.

After exposure of the charge to the action of the dehydrogenating catalyst for a time which may vary from 0.2 to 30 seconds, depending on the refractoriness of the charge and the conditions employed, the effluent vapors are fractionated to separate the olefins formed as overhead vapors. The unreacted parafllns may be returned to the preheater as recycle. The higher the molecular weight, of the paraffin stock the lower its resistance to dehydrogenatlon and cyclization. Nonanes and decanes, for example, are more reactive than pentane and hexane, and require less severe reaction conditions to obtain the desired conversion.

The olefin fraction thus recovered may be passed through a cooler and, if steam was employed as a diluent in the dehydrogenation zone,

through a dryer unit to remove liquid and vapor water, and may be then passed into contact with the cyclization catalyst, which may be either metallic oxides or amphoteric metal halides. Anhydrous aluminum chloride is a preferred catalyst. When it is used, the temperature range is controlled carefully to obtain a maximum of' cyclization to the cycloparaflins and to minimize polymerization and aromatization of the olens. At temperatures of the order of zero C. and lower, heavy polymers of boiling range corresponding to lubricating oils are formed in preponderant amounts. As temperatures approach 375- 400 C. (about 'ZOO-750 F.) the reaction minimizes polymerization, and cracking reactions increase along with formation of progressively heavier hydrocarbon-AlCla addition products.

Temperature therefore must be controlled within a range which promotes the formation of simple cycloparamns, minimizing both dehydrogenation to aromatlcs and multipolymerization to heavy, viscous products. Here the presence of the diluent hydrogen and hydrocarbon or other gases aids also in retarding these undef sirable reactions and in furthering cyclization. Temperatures in this reaction are therefore of the order of D-400 F., the range maintained depending on the hydrocarbons processed and their relative resistance to cyclization, heavier hydrocarbons requiring lower temperatures and shorter contact times than the lighter Cs and Ce oleflns. The effluent from this step, in which contact times may vary from 0.1 second to 15 seconds or more, is fractionated to recover the unreacted oleflns and diluent hydrogen-hydrocarbon gases, and the raw product, including cycloparaffins, aromatics and heavier aromatization and polymerization products, may be ref'ractionated to remove the heavier undesirable materials for recycle. This heavy material rnaybe eliminated from the system or may be cracked or otherwise processed to produce recycle materials as desired. The rectified cycloparafiins and lighter aromatics, the latter formed as by-products, may be sent to storage as finished product except for any desired chemical purification.

rThe foregoing description may be more fully understood by reference to Fig. l of the drawings. Parailln charge stock, which may consist of essentially one hydrocarbon, as normal hexane, or a mixture of several hydrocarbons, is mixed with recycle material in line I, enters the preheater 2, is heated to the desired temperature and passes through line 3 to the dehydrogenation chamber, 4, after dilution with hydrogen-hydrocarbon light material, or other diluent from line 5. The eiiluent vapors from the dehydrogenator are discharged through line 6 to fractionator 1. Bottoms from this tower are stripped of lighter material in reboiler 8 and are returned as recycle through line 9. The overhead olefins pass through line I0 to cooler II and dryer I2, where the temperature is reduced to that required in the next step, and water, if present as condensate or for any other reason, is eliminated. Reflux is returned to fractionator I through line I3, and the remainder of the olefin charge is blended with olefin recycle and any desired additional hydrogen-hydrocarbon diluent in line I4 and enters the cyclization chamber where it contacts the cyclization catalyst in any desired form. Reaction products are discharged through line I6 to the fractionator I1, where the raw cyclics-aromatics content is condensed, stripped of lighter material in reboiler I8 and is withdrawn through line I9. Unreacted oleflns and light diluent material are taken overhead through line 20 to con denser 2|, where recycle olefins are condensed and withdrawn through line 22, reflux being drawn off for return to the fractionator l1 through line 23. Uncondensed hydrogen and light hydrocarbon gases (C1 to C) are returned to line 5 and the reaction system.

Pressures as high as atmospheres or about 1500 pounds per square inch may be advantageous in the first or dehydrogenating step; up to '75 atmospheres, or about 1000 pounds per square inch, may be used in the second step, though the pressure in this step may be considerably lower than those indicated when reacting Cs, Cs and Cv hydrocarbons.

The essential features ofthe embodiment of the invention represented in Fig. 2 include catalytically cracking heavier oils, preferably using a metal halide catalyst, provided this step is desired to obtain charge stock for the main part of the process; introducing the Ce-Cn aliphatic (chieiiy paraillnic) hydrocarbon fraction of the cracking effluent to a catalytic dehydrogenatorisomerizer where the initial rearranging reaction is carried out, preferably in the presence of a metal halide catalyst, whereby compounds, largely olefins, are formed which are adapted to be converted to cyclic compounds; transferring the desired fraction of these reaction products asazoso to a second reaction chamber where they are cyclized in the presence of diluent gases rich in hydrogen, with some aromatization, and frequently with some aikylation as the result oi' side reactions; tractionating the reaction products from each zone to concentrate the material for the next step, to obtain unreacted material for recycle to the same step, or to obtain the final product. The first reaction is controlled to produce intermediate reaction materials, which may include olefins and partially reacted materials which are optimum charge stock for the next or cyclizing step, and the reactions are arrested before any considerable portion has been either aromatized or saturated to a point which makes it unsatisfactory for the reaction desired in the next step. The reactions taking place involve dehydrogenation of the parailins to those olefins which are adapted to be cycllzed and lsomerization of any oleflns present to those forms which may be readily and directly cyclized.

In the case where satisfactory charge stock of the required molecular weight, either a single paraffin or isoparaiiln hydrocarbon or a mixture of hydrocarbons, is available from reilnery or other plane streams or other outside sources in volume suiilcient to meet the throughput requirements of the cyclization unit, the rst step described above (l. e., the catalytic cracking step) may be omitted. Or, the first step may be used to obtain additional charge stock to augment that available from outside sources. Or, the nrst or cracking step may be employed to supply the entire charge stock for the unit.

Conditions employed in the cracking step are controlled to produce a maximum of the hydrocarbons desired. The higher the temperature and pressure the lower the molecular weight of the main body of product. The temperature range is between about 650 and about 850 F. If a preponderance of heavier hydrocarbons in the range mentioned is desired the cracking temperature should be maintained in the lower portion of this range, with correspondingly higher pressures; if butanes, pentanes and hexanes are desired in greater percentage a higher temperature and in general lower pressure are employed. Careful control of these conditions, along with simultaneous control of the average time of contact of the charge stock with the catalyst, over a considerable range, is employed in order to control the average molecular weight of the parafilns, isoparaffins and/or aromatics formed from the heavy charge such as gas oil, keroslne, heavy cyclics and so on.

Efuent from the cracking zone is preferably fractionated in two different fractionators, the first to separate the heavier, insuihciently cracked material for recycle, the second stage to separate light gases, i. e. hydrogen and light noncondensable gases, which may be added later as a diluent and hydrogen supplier or may be discarded from the system as the details of operation may make desirable. More frequently this diluent iight material will be discarded from the system, although in the embodiment shown in Fig. 2 of the accompanying drawings it is shown as being returned to the system at a later point as diluent, merely as an illustration of one alternative method of operation.

Fresh Cef-Cn hydrocarbons from outside sources, in any combination or mixture of these hydrocarbons, may be added at this point, or it may be the beginning of the operation, in case the cracking reaction is not employed to supply part or all o! the charge material. The incoming fresh C to Cu hydrocarbons may be introduced into a preliminary iractionator it such concentration of the desired hydrocarbons is to be made as a part of this operation, or may be introduced directly in the rst reactor chamber, if the charge has the desired composition. This charge, or combined charge materials, in the event the charge is obtained from more than one source, enters a rst reactor Where several reactions may occur in varying degrees, including oleflnic unsaturation, isomerization and apparently formation of unstable complexes including the rupture of heavier molecules to form, for example, a parailin or isoparafln and an olen, unstable cross-linkages between carbons of the same or diierent molecules, and other probable reactions not well understood. This step and the second or cyclizing or aromatizing step are carried out separately from one another in order that conditions optimum for each reaction and for the furtherance of the ilnal result may be accomplished with greater yields and smaller percentages of byproducts. For the rst reaction, temperatures should be maintained approximately within the range 50G-600 F., and intermediate pressures of from 'atmospheric pressure up to 100 pounds per square inch gauge, to effect a re-forming action on the hydrocarbons processed.

The eilluent from this first chamber may be fractionated to return recycle to the chamber. The very light hydrocarbons, methane to propane, and preferably to'butane, along with free hydrogen may be vented from the system or may be continued as diluent into the second step as the balance of diluent-reaction mixture may be desired. The partially reacted charge, consisting of the Gs to Cn fraction of the eiiluent from the first chamber, then is introduced into a second chamber, meeting fresh catalyst as outlined later herein and is reacted at lower temperatures and higher pressures, of the order of 50-400" F. and 50-250 pounds per square inch gauge pressure, conditions which promote cyolization of the partially reacted materials from the first step and which minimize but do not necessarily eliminate formation of aromatic hydrocarbons. To increase the contact time and therefore permit employment of lower temperatures but to increase the yield-per-pass, two or more chambers in series may be employed with advantage in carrying out the second step. In a nal traction the main body of reaction products, cyclics and aromatics, including products heavier than those desired from recycle material to this second or to the rst step, are separated. Any surplus of very light materials may be vented or returned to steps earlier in the system.

The amount oi diluent employed is varied from a few per cent to as much as 50 per cent, depending on the composition of the charge, contact time and temperatures and pressures employed. In general the greater the amount of diluent ernployed in the cyclizing step of my invention the less the tendency toward polymerization and simiiar reactions, which form larger molecules and thus defeat the` purpose of the invention. However, ii diluent and hydrogen percentage present are too high, the tendency is toward a hydrogenation reaction to the exclusion of cyclization and aromatization. which also defeats the purpose of the invention. All operating conditions, therefore, are controlled to carry the reaction desired between the two undesirable ends of oversaturation to form non-cyclic paraiiins. on the one hand, and unsaturation to form high proportions of aromatics and polymeric products, on the other. The high selectivity of the action of the catalyst is taken advantage of to the fullest extent by exact control of operating conditions as outlined herein.

The metal halide, such as aluminum chloride, may be used in the form of a slurry, easily transportable from one vessel to the other. or it may be installed in the chambers in solid form, and by a system of manifolding, the sequence of the flow oi charge through the system may be made to follow the countercurrent principle of contact which is shown for illustrative purposes in the drawings. In either case, the catalyst is in countercurrent relationship to the charge, progressing from lower to higher temperatures in the process. Fresh catalyst is introduced into the cyclization step of the process, progresses to the reforming step. and thence. if heavier oils are cracked to supply low-molecuiar-weight charge stock. the catalyst is employed at the relatively high cracking temperatures as outlined. When spent in `this step the catalyst may be discarded or regenerated as desired. In this way the catalyst is used successively under increasingly stringent or severe reaction conditions whereby any spending in the zone from which it comes is overcome.

It must be kept in mind that the principle of this invention is not dependent on nor limited by any theoretical considerations or explanations of what occurs in either the unsaturator step or in the cyclizing step, particularly the nature of the reactions in the unsaturator or reforming step. The intermediate reactions occurring during the action of aluminum chloride and other metal chlorides on hydrocarbons are extremely complex, and not well understood. Arresting these reactions by any practicable meansat different stages of the reaction cycle produces a variety of materials or reaction products from any given combination of charge stocks. Experience has shown that separating this part of the operation into two steps, each operated under the optimumset of conditions for effecting the desired result, gives better results and higher yields of the nal products desired. and also gives greater exibility to the process than does an attempt bons desired. and the entire charge is flashed, through line |03 into fractionator |04, from which uncracked or insuiciently cracked material is recycled to the cracking zone through line |05. Cracked vapors are transferred through line |06 to the second fractionator |01 from which very light hydrocarbons and hydrogen are taken overhead through line |00 and rectified distillate iconsisting essentially of C5 to Cm parafins and olens) is transferred through line i509 to the first reactor' chamber i l0. Fresh charge from any outside source is admitted here, either through line directly to the reactor or through line ||2 to the second fractionator |01, in case this charge requires rectification before further processing is undertaken.

After contacting the catalyst in reactor l0 the reaction products may be admitted through line H3 to fractionator H4 if it is desired to eliminate very light products, or this fractionator may be bypassed. Light products may be removed through line H6, recycle stock may be returned through line H6 to the rst reactor |20, or the entire charge may be passed through line ill to the rst section ||9 of the second reactor, after admixing with it diluent containing hydrogen through line I i8. This reactor may be in two or more sections, the reaction products and unreacted material from the rst section passing into the second section |20, and so on. in which fresh catalyst is contacted in countercurrent flow relationship. As a further control means, for stopping the reaction after the charge has passed through the last reactor, cold diluent liquid and/ or vapor is added through line |2| to shockchill the reaction products which pass through line |22 to final iractionator |23 from which diluent is returned for recycle or is discarded. through lines |24 and |25 or |26. respectively.

dolnsufiiciently reacted material is returned for recycle to any section or sections of the second reactor through line |21 while cyclic and other products which require no further processing are withdrawn from the system through line |28. In

the event that heavy material is present in this to carry out the complete set of reactions of un- 5 saturating and cyclizing the hydrocarbons in a single step or reaction zone. The reaction mixture transferred from the unsaturator to the cyclization zone may contain a complex mixture of aluminum chloride-hydrocarbon combination products, olens. paraflns and isoparaiilns and other products, the chemistry and the composition of which is not well understood. The invention, therefore. comprises the accomplishment of the series of reactions which give the final products without being limited in any way by any theoretical or scientic explanation or by the lack of such explanation.

Details of this process of the invention may be followed more clearly by reference to Fig. 2 of the accompanying drawings, which illustrates one preferred method for practicing this invention. Heavy oil such as gas oil, kerosine, heavy polymer-cyclate or other similar charge is admitted to the system through line |0| to cracking chamber |02 after admixture with recycle stock from fractionator |04 through line |05. The charge is cracked in contact with metal halide catalyst. such as anhydrous aluminum chloride, conditions being controlled to produce the hydrocarproduct, which should be reprocessed, the stream may be further fractionated in equipment not shown in the drawing to remove this heavier material, which may be returned to the cracking zone or used for any other purpose. In case a mixture of hydrocarbon products, mixed with unreacted material, is obtained from the nnal reactor. multiple fractionation is necessary to yield recycle and finished materials.

The catalyst, in this preferred embodiment of the invention, is introduced into the system through line |28 into the cyclization zone and thereafter passes through the system in countercurrent relationship to the path or flow of the charge stock. If the catalyst is in slurry form it is circulated through the cyclization chamber |20 by means of any convenient pumping arrangement, slurry being returned via line |30 to line |29, after passing through the reaction chamber. Continuously a predetermined portion of the catalyst stream is withdrawn through line |3| to cycle through the next section or reaction chamber I I9 through line |32 and recycle through line |33. In turn a portion is withdrawn continuously to the unsaturator chamber ||0 through line |34, is recycled in that zone through line |35 downward through the chamber and returned through line |36. When the activity of the catalyst in this section of the process is reduced to an unsatisfactory level it is Withdrawn, a conassignee tinuous operation in practice, through line |31 to the cracking section Il! of the unit. is recycled therethrough through line ill, the reaction chamber, and line |39. Spent catalyst is withdrawn to discard or for regeneration through line For simplicity, preheaters, coolers and other accessory equipment are eliminated from Fig. 2cf the drawings.

The preferred procedure in this embodiment of the invention is to employ anhydrous aluminum chloride. If this catalyst is used, the temperature range in the necessary zones is controlled carefully to obtain a maximum of cyclization and to minimize polymerization. At temperatures of the order of 32 F. (0 C.) and lower, heavy polymers of boiling range corresponding to lubricating oils are formed in preponderant amounts. As temperatures approach 70D-750 F. (about 375-400" C.) the reaction minimizes polymerization, and cracking reactions increase along with formation of progressively heavier hydrocarbon- AlCh addition products. Temperature therefore must be controlled within a range which promotes the formation of simple cyclics, i. e., cycloparaifins, minimizing both dehydrogenation to aromatics and multipolymerization to heavy, viscous products. Here the presence of the diluent hydrogen and hydrocarbon or other gases aids also in retarding these undesirable reactions and in furthering the desired cyclization. Temperatures in the cyclization reaction are therefore of the order of 20D-400 F. (about 90-200 CJ, the range maintained depending on the hydrocarbons processed and their relative resistance to cyclization, heavier hydrocarbons requiring lower temperatures and shorter contact times than the lighter C5 and Ce olens. Contact timeg may vary from 0.1 .second to seconds or more. The eiiiuent from this step is fractionated to recover the unreacted olefins and diluent hydrogen-hydrocarbon gases, and the raw product, including cycloparaflins, aromatlcs and heavier aromatization and polymerization products, may be refractionated to remove the heavier undesirable materials for recycle, which may be either eliminated from the system or may be cracked or otherwise processed to produce recycle materials as desired. The rectified cyclics (cycloparaiiins) and lighter aromatics, the latter formed as byproducts, may be sent to storage as finished product except for any desired chemical purification. If desired the cycloparaiilns and the aromatics may be separated.

I have found that low pressures and high temperatures, with or without catalysts, tend toward the formation of more aromatic hydrocarbons, increasing the degree of dehydrogenation which accompanies cyclization. The converse of these conditions, combined with the diluent effect of the hydrogen and hydrocarbon vapors, and the displacement of the dehydrogenation-hydrogenation reaction equilibrium in the direction oi' less severe dehydrogenation because of the excess hydrogen employed., will in general promote the limitation of dehydrogenation to the simpler monoolefin formation and the production of cycloparaflins rather than aromatics, the more highly unsaturated cyclics. Thus higher pressures may be employed preferably in these reactions to the advantage of cycioparaflin production, and correspondingly lower temperatures will suffice for accomplishing the preferred results as indicated.

In cyclizing paraflins or oleflns, the greater tendency is to form either five or six-membered rings. For example, when cyciizing hexene-l either cyclohexane or methylcyclopentane may be formed, with the greater tendency toward the six-carbon ring. If the double bond is broken in the olefin and the bond on the terminal carbon displaces a hydrogen atom on the opposite terminal carbon, a six-carbon ring results, the displaced hydrogen atom satisfying the free bond on the beta-carbon atom. If the broken bond of the beta-carbon unites with the opposite terminal carbon, methylcyclopentane is formed. It is theoretically possible that a dimethyl or trimethyl-substituted ring may be formed by combining the beta-carbon bond with a carbon within the chain, other than the opposite terminal carbon; however, the tendency to form either, ve or six-carbon rings is strong, to the comparative exclusion of other reactions. Heptanes. octanes and hydrocarbons of higher molecular weight also tend to form alkyl-substituted five and six-carbon rings, with the extra methyl or methylene groups forming first a single straight side chain, which may break down into two or more disubstituted methyl groups. I have found that normal octane, for example, will rst form ethylcyclohexane, carbons seven and eight with attache'd hydrogen atoms forming a single ethyl side chain. Continued exposure to reaction conditions may cause a rupture of this side chain to form two methyl groups, one of which displaces a hydrogen on the nucleus, forming dimethylcyclohexane, with the methyl groups in the ortho, meta or para positions. more frequently the ortho position. Other variations of this formation may occur, by the combination of free methyl or other alkyl groups with the cycloparafiin nuclei formed in the main reaction. 'I'he tendency, therefore, in this invention is toward the formation of ve and six-membered carbon rings 0f the generic formula CnHzn, with or without side-chain substituents, depending on operating conditions and the composition of the charge stock.

This description of my process and invention outlines the principles on which the invention is based, and indicates preferred catalysts and methods for carrying out the invention. 'Ihe principles of the invention are broad, however, and a large number of variations are permissible in operating the process with good results and within the limits set by these principles and the appended claims.

I claim:

1. A process for the production of cycloparamn and aromatic hydrocarbons from paraffin hydrocarbons, which comprises subjecting a C5 to C1: paraffin hydrocarbon fraction in a dehydrogenation zone at a dehydrogenation temperature and pressure to the action of an aluminum chloride catalyst to convert it to an intermediate hydrocarbon material adapted for cyciization, recovering a fraction comprising Cs to C1: olefin hydrocarbons from the eilluent of the dehydrogenation zone and subjecting said fraction to cyclization in a cyclization zone at a cyclization temperature and pressure in the presence of an aluminum chloride catalyst to effect cyclization of a substantial portion of said olefin-containing fraction, fractionating the eilluent from said cyclization zone to recover cyclic hydrocarbons therein, recovering fractions comprising a mixture of hydrogen and light hydrocarbon gases from each of said dehydrogenation and cyclization eflluents and passing a portion of at least one of said fractions into each of said dehydrogemtion and said cyclization zones in such amounts as to act as a diluent therein and to prevent polymerization without engendering substantial hydrogenation to the exclusion of cyclization of the olen hydrocarbons therein, shock-cooling the eiiiuent from said cyclization zone with a further cooled portion of one of said fractions comprising hydrogen and light hydrocarbon gases, introducing fresh aluminum chloride catalyst to said cyclization zone and circulating it therein, withdrawing a portion of the aluminum chloride catalyst from said cyclization zone and introducing and circulating it in said dehydrogenation zone, and withdrawing spent aluminum chloride catalyst from said dehydrogenation zone in an amount substantially equivalent to the amount of fresh cataiyst introduced to said cyciization zone.

2. A process for the production of cycloparatiin and aromatic hydrocarbons from paraiiln hydrocarbons, which comprises subjecting a Cs to Cia parafiln hydrocarbon fraction in a dehydrogenation zone at a temperature within the range oi approximately 500 to approximately 600 F. and a pressure within the range of approximately 0 to approximately 100 pounds per square inch gauge to the action o! an aluminum chloride catalyst to convert it to an intermediate hydrocarbon' material adapted for cyclization. recovering a fraction comprising Cs to Ci'.` oleiln hydrocarbons from the eilluent of the dehydrogenation zone and subjecting said fraction to cyclization in a cyclization zone at a temperature within the range of approximately 200 to approximately 400 F. and an elevated pressure within the range oi' approximately 50 to approximately 250 pounds per square inch gauge in the presence of an aluminum chloride catalyst to eect cyclization of a substantial portion of said oleiin-containlng traction, fractionating the eiiiuent from said cyclization zone to recover cyclic hydrocarbons therein. recovering fractions comprising a mixture of hydrogen and light hydrocarbon gases from each of said dehydrogenation and cyclization eiiiuents and passing a portion of at least one of said iractions into each of said dehydrogenation and said cyclizatlon zones in such amounts as to act as a diiuent therein and to prevent polymerization without engendering substantial hydrogenation to the exclusion of cyclization of the olen hydrocarbons therein, shock-cooling the emuent from said cyclization zone with a further cooled portion of one of said fractions comprisingr hydrogen and light hydrocarbon gases, introducing fresh aluminum chloride catalyst to said cyclization zone and circulating it therein, withdrawing a portion of the aluminum chloride catalyst from said cyciizatlon zone and introducing and circulating it in said dehydrogenation zone, and withdrawing spent aluminum chloride catalyst from said dehydrogenation zone in an amount substantially equivalent to the amount 0f fresh catalyst introduced to said cyclization zone.

3. A process as denned in claim 2 and further characterized in that the fractions comprising hydrogen and light hydrocarbon gases which are used as diluents in the dehydrogenation and cyciization zones are composed of a mixture consisting essentially of hydrocarbons having from one to four carbon atoms per molecule and containing from approximately 10 to approximately 5D per cent of hydrogen.

ARCH L. FOSTER.

CERTIFICATE OF CORRECTION.

Ptent NO. 245873989 October 50 9115.

ARCH L. FOSTER.

It is hereby certifie of the above num ond column, line 51, for (C1 to C- those" read these;' and that the this correction therein that th in the Patent Office 'd that error appears in the printed specification bered patent requiring correction` as follada: Page ii, secread (C1 to C line 59, for

said Letters Patent should be read with e same may conform to the record of the case Signed and sealed this 5th day of February, A. D. 19M).

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

cyclization zones in such amounts as to act as a diluent therein and to prevent polymerization without engendering substantial hydrogenation to the exclusion of cyclization of the olen hydrocarbons therein, shock-cooling the eiiiuent from said cyclization zone with a further cooled portion of one of said fractions comprising hydrogen and light hydrocarbon gases, introducing fresh aluminum chloride catalyst to said cyclization zone and circulating it therein, withdrawing a portion of the aluminum chloride catalyst from said cyclization zone and introducing and circulating it in said dehydrogenation zone, and withdrawing spent aluminum chloride catalyst from said dehydrogenation zone in an amount substantially equivalent to the amount of fresh cataiyst introduced to said cyciization zone.

2. A process for the production of cycloparatiin and aromatic hydrocarbons from paraiiln hydrocarbons, which comprises subjecting a Cs to Cia parafiln hydrocarbon fraction in a dehydrogenation zone at a temperature within the range oi approximately 500 to approximately 600 F. and a pressure within the range of approximately 0 to approximately 100 pounds per square inch gauge to the action o! an aluminum chloride catalyst to convert it to an intermediate hydrocarbon' material adapted for cyclization. recovering a fraction comprising Cs to Ci'.` oleiln hydrocarbons from the eilluent of the dehydrogenation zone and subjecting said fraction to cyclization in a cyclization zone at a temperature within the range of approximately 200 to approximately 400 F. and an elevated pressure within the range oi' approximately 50 to approximately 250 pounds per square inch gauge in the presence of an aluminum chloride catalyst to eect cyclization of a substantial portion of said oleiin-containlng traction, fractionating the eiiiuent from said cyclization zone to recover cyclic hydrocarbons therein. recovering fractions comprising a mixture of hydrogen and light hydrocarbon gases from each of said dehydrogenation and cyclization eiiiuents and passing a portion of at least one of said iractions into each of said dehydrogenation and said cyclizatlon zones in such amounts as to act as a diiuent therein and to prevent polymerization without engendering substantial hydrogenation to the exclusion of cyclization of the olen hydrocarbons therein, shock-cooling the emuent from said cyclization zone with a further cooled portion of one of said fractions comprisingr hydrogen and light hydrocarbon gases, introducing fresh aluminum chloride catalyst to said cyclization zone and circulating it therein, withdrawing a portion of the aluminum chloride catalyst from said cyciizatlon zone and introducing and circulating it in said dehydrogenation zone, and withdrawing spent aluminum chloride catalyst from said dehydrogenation zone in an amount substantially equivalent to the amount 0f fresh catalyst introduced to said cyclization zone.

3. A process as denned in claim 2 and further characterized in that the fractions comprising hydrogen and light hydrocarbon gases which are used as diluents in the dehydrogenation and cyciization zones are composed of a mixture consisting essentially of hydrocarbons having from one to four carbon atoms per molecule and containing from approximately 10 to approximately 5D per cent of hydrogen.

ARCH L. FOSTER.

CERTIFICATE OF CORRECTION.

Ptent NO. 245873989 Gotooer 50 9115.

ARCH L. FOSTER.

It is hereby certifie of the above num ond column, line 51, for (C1 to C- those" read these;' and that the this correction therein that th in the Patent Office 'd that error appears in the printed specification bered patent requiring correction` as follada: Page ii, secread (C1 to C line 59, for

said Letters Patent should be read with e same may conform to the record of the case Signed and sealed this 5th day of February, A. D. 19M).

(Seal) Leslie Frazer First Assistant Commissioner of Patents. 

